In radio communication devices, for example, it is necessary to reduce second-order distortion in received signals. When a single balanced mixer having a pair of MOS transistors is used, even the transistors placed adjacent to each other on a chip have significantly different threshold voltages, which may cause second-order distortion. In order to overcome the disadvantage of variation in the threshold voltages of the transistors, there is a measure of providing an additional circuit. For example, there is a method of providing means for calibrating the DC bias in an input unit of a direct-conversion mixer, for calibrating the DC bias of thresholds set for a reception level and a transmission power to reduce the influence of the second-order distortion. With such a technique requiring the additional circuit, however, the circuitry for the adjustment will be very complicated and large, which will undermine the advantage that direct conversion mixers are small in size.
A few group reports a measure to suppress variation in the threshold voltages using memory transistors. There have been however, no discussions on data retention characteristics that are one of the most important characteristics of memory transistors in the reports on threshold variation compensating circuits using memory transistors proposed so far. Circuits in which threshold variation is compensated are desired to have sufficient data retention characteristics.